This invention relates to forming a hard, protective surface on a body, and, more particularly, to forming a phosphate-bonded layer at the surface of the body.
In many applications, a light, strong, fracture-resistant material with a hard, erosion-resistant surface is desired. For example, an externally exposed component of an aircraft should be light, strong, and tough, so that it does not fracture easily under loadings. The component should also be resistant to erosion resulting from particulate matter in the air, which, due to its high velocity, can rapidly wear away unprotected surfaces.
The objectives of light weight, high strength and fracture resistance, on the one hand, and surface erosion resistance, on the other hand, are often difficult to attain in a single, unitary piece of material. Light-weight, fracture-resistant materials usually include at least some relatively soft, ductile phases or components that are readily worn away at the exposed surfaces. Conversely, hard, erosion-resistant materials usually exhibit low ductilities and fracture properties.
To overcome these difficulties, it is well known to use light-weight, high-strength, fracture-resistant materials for structural components, but to protect the surface of the components with erosion-resistant surface layers. In some cases, the erosion-resistant surface layers are in the form of coatings of ceramic-based materials that are bonded to the components at their surfaces. In other cases, the surface layers are obtained by modifying the basic structure of the component at its surface, as by carborizing or the like. In one approach, a ceramic material such as alumina or silica is formed at the surface of the component to be protected. Alumina has the virtue of being hard and erosion resistant, but also resistant in chemical erosion and oxidation.
Many different surface treatment techniques are known. However, there always remains the desire and need to further improve the results by increasing the hardness and erosion resistance of the surface without sacrificing its other desirable properties. The present invention fulfills this need, and further provides related advantages.